The present invention relates to an air bag system for an automotive front passenger seat and, more particularly, to an air bag system which detects a certain level of impact on collision of the automobile and causes a gas to be produced from an inflator that is a gas generator so as to inflate an air bag, thus constraining a passenger seated on the front passenger seat.
One kind of an air bag system for an automotive front passenger seat is a vertical type air bag system comprising an air bag case, an inflator mounted under the bag case, and an air bag mounted above it. In a lateral type air bag system, an inflator is located on one side in an air bag case. An air bag and the inflator are arranged side by side in a direction parallel to the plane of the opening in the air bag case. Various lateral type air bag systems including this kind have been proposed. These proposed systems are discussed in detail below.
One kind of lateral type air bag system has been devised by the present applicant and is described in Japanese Patent Laid-Open No. 191362/1994. This system has an air bag case which opens to a substantially horizontal surface of an automotive instrument panel. An inflator and a zigzag folded air bag are mounted inside the air bag case such that the inflator is positioned ahead of the bag, i.e., the inflator is located closer to the front of the vehicle. An unfolded flat bag portion extends over the inflator. The inflator is provided with gas support ports which are located at a front upper position and a rear lower position, respectively, in a horizontal cross section of the inflator.
In the operation of this air bag system, when a gas is produced from the inflator, the unfolded flat bag portion which is located immediately above the inflator begins to inflate. Therefore, the upper portion of the bag expands upward first and swells into the space defined by the windshield extending obliquely and also by the instrument panel. As a result, the upper portion of the air bag assumes a given shape. Subsequently, the lower portion of the air bag expands. Consequently, the whole bag expands into a desired three-dimensional shape.
An example of a method for folding an air bag is seen in an air bag system described in Japanese Patent Laid-Open No. 227353/1994, also invented by the present applicant. An embodiment of this air bag system is similar in structure to the air bag system described in the above-cited Japanese Patent Laid-Open No. 191362/1994 except that an air bag disposed in a side-by-side relation to an inflator inside an air bag case has an upper, zigzag folded portion adjacent to the inflator and a lower portion which is adjacent to the upper portion and wound into a roll. When the gas is produced from the inflator, the zigzag folded portion loosens more easily than the lower wound portion. By making use of this fact, the upper portion of the air bag expands first when the gas is produced from the inflator. Subsequently, the lower portion expands. As a result, the whole structure swells into a desired three-dimensional shape.
These well-known techniques control the behavior of expansion of an air bag, by taking notice of the structure of a module.
In U.S. Pat. No. 5,405,164 (Japanese Utility Model No. 3014497), a diffuser is located over an inflator with a space between them. This inflator is shaped like a bottle. A gas is ejected from around a port formed at one side of the inflator. This is a so-called hybrid inflator. Since the gas injection portion is distributed unevenly in this way, the diffuser is mounted to regulate the flow of the gas from the port. Specifically, the diffuser is provided with minute holes in positions corresponding to the opening in the inflator. The diameter of the holes increases away from the opening.
Japanese Patent Publication No. 78052/1994 (U.S. Pat. No. 4,998,751) discloses a technique for causing an inflator to exhibit an S-shaped output characteristic curve. In particular, this publication says, xe2x80x9cIt is an object of the present invention to provide an improved two-chamber expansion system for imparting an S-shaped pressure-time performance curve to an air bag which protects an automotive passenger. In this expansion system, charges of a gas-generating agent in the chambers are simultaneously ignited by a single blasting device. It is a more specific object of the present invention to provide a two-chamber expansion system which delays ignition of the gas-generating agent in the second chamber after the gas-generating agent in the first chamber is ignited, the expansion system being further characterized in that the duration of the delay is achieved by the structure and shape of the blasting device.xe2x80x9d (column 7, lines 9-17). This system is capable of expanding the air bag slowly at first to mildly push the passenger if he or she is a child assuming an inappropriate posture. Then, a controlled, released gas is supplied into the air bag so as to expand the bag quickly to protect the seated passenger, irrespective of his or her build (column 17, lines 34-38). The output characteristic curve is shaped into an S-shaped form by adopting this inflator. That is, the output of the inflator can be made low at first. However, the effect of the S-shaped characteristic curve may be lessened, depending on the structure of the module located downstream of the inflator as viewed from the injected gas stream. Furthermore, the bag is not expanded mildly throughout the process of expansion.
These air bag systems control the behavior of expansion of air bags, by taking notice of only the inflator output and the regulation provided by the diffuser.
It is a first object of the present invention to provide an air bag system which inflates an air bag mildly during its initial phase of expansion by finding a correlation between the inflator output characteristic and a modular structure. It is a second object of the invention to permit the air bag to be inflated mildly during all phases of the inflation of the air bag.
The present invention is intended to achieve these objects. An air bag system is provided that includes an air bag case having an opening on a top side, an inflator disposed inside the air bag case, a folded air bag juxtaposed to the inflator and disposed behind the inflator inside the air bag case (i.e., the air bag is located closer to the rear of the vehicle than the inflator), and a diffuser for regulating a stream of a gas from the inflator. The diffuser is located between the inflator and the opening in the air bag case, and is provided with a plurality of gas supply nozzles or holes. A space is created between the outer surface of the inflator and the diffuser at least when the gas is produced from the inflator.
The diffuser may be made of a metal or other rigid substance. Furthermore, the diffuser may be made of cloth or other soft material. In the latter case, when the air bag has been folded, the diffuser is in intimate contact with the outer surface of the inflator. However, when the gas is being produced from the inflator, the diffuser is also inflated, thus creating the space between the diffuser and the inflator.
Since this air bag system is equipped with the diffuser, the gas spouted from the inflator is temporarily stored in the space between the inflator and the diffuser. The stored gas is mildly supplied as a regulated stream from openings in the diffuser into the air bag. For this purpose, the space between the inflator and the diffuser preferably has a volume adapted to temporarily store the gas produced from the inflator. Furthermore, it is desired to appropriately determine the number of the holes, or openings, in the diffuser, the total area of the holes, and their positional relationship. The amount of the gas exhausted is made uniform over the whole outer surface of the diffuser.
In another feature of this air bag system, the inflator and the air bag are arranged side by side. Consequently, the upper portion of the air bag is inflated first. Then, the lower portion is inflated. Hence, mild expansion is accomplished.
The air bag disposed in the air bag system has a folded portion which can comprise an upper zigzag folded portion and a lower portion wound into a roll. The upper portion is adjacent to the inflator. The lower portion is adjacent to the upper portion. In this structure, when a gas is supplied into the air bag, the upper zigzag portion of the air bag inflates first. Then, the lower coiled portion inflates. As a consequence, milder expansion of the whole air bag is achieved.
This air bag system can be of a so-called top-mounted type. In this case, the opening in the air bag case lies in a substantially horizontal surface of an instrument panel. Accordingly, the gas meets the surface of the flat portion located over the inflator, i.e., the unfolded portion, and this portion first inflates. Then, this flat portion and the following upper portion of the folded portion swell into a space defined by a windshield and the instrument panel. As a result, a desired two-dimensional spread is obtained. Subsequently, the following lower portion of the folded portion swells in such a way as to grow downwards from the upper portion of the air bag inflated in two dimensions. Consequently, the air bag inflates into the desired three-dimensional shape.
Let Qt be the total amount of gas produced during a time interval between 0 and t msec. Let A be the cross-sectional area of the opening in the air bag case. In this air bag system, the ratio Qt/A preferably varies in several stages as given below.
This makes it possible to inflate the whole air bag mildly. In the above relations, the total amount Qt of the produced gas is an apparent volume depending on the number of moles produced and amount of heat.
In this air bag system, the inflator may have two or more squibs (electric detonators). In this case, a delay time can be introduced in the ignition time, and the output can be adjusted. More specifically, generation of the gas from the inflator is carried out in two stages. As a consequence, the whole air bag is inflated more mildly. In addition, the inflator may also be a hybrid inflator having the two or more squibs as described above and two or more associated gas generators each containing an explosive charge and a gas-generating agent. Thus, the inflator is charged with a compressed gas.
Generally, it is advantageous for this air bag system to use a so-called hybrid inflator. Normally, heat is utilized to expand a gas. Inflators are broadly classified into two major categories: pyrotechnique inflator and hybrid inflator. The former makes use of pyrotechnics, i.e., explosive charges. Typical examples are described in the above-cited Japanese Patent Publication No. 78052/1994, in which an S-shaped curve is achieved with a pyrotechnique inflator. The latter consists of a bottle-like container mainly charged with a pressurized gas and a gas propellant, and is cited in the abovementioned U.S. Pat. No. 5,405,164. Specifically, a squib is mounted in the opening at one end of the bottle-like container. The squib is excited by an electrical signal. Then, a sagittal member disposed adjacent to the squib is moved axially through the container. This breaks a pressure partition that isolates the pressurized gas from the outside atmosphere. Then, the pressurized gas is produced through the opening and supplied into the air bag. The sagittal member also acts on the explosive charge. The result is that the gas-generating agent placed around the explosive charge is reacted, thus giving heat to the pressurized gas. The expansion of the gas is promoted further. In this way, the hybrid inflator is little assisted by heat during an initial phase of generation of the gas. This initial phase corresponds to the initial phase of the expansion of the air bag. Therefore, the output characteristic of the hybrid inflator produced during this time interval is more easily adjusted mechanically and dimensionally than the pyrotechnique inflator which depends chiefly on a chemical reaction.
On the other hand, where the diffuser is adjusted to adjust the gas finally entering the air bag, it is necessary to adjust the volume of the space between the inflator and the diffuser. However, this approach has limitations, since a space accommodating the bag must be secured. Furthermore, the total area of the nozzles or holes, their arrangement, and other factors must be adjusted. In this way, various limitations exist. Accordingly, it is desired to adopt a hybrid inflator whose output is easily matched to these limitations.
Other objects and features of the invention will appear in the course of the description thereof, which follows.